| Document and Entity Information | Oct. 29, 2020 |
| Document and Entity Information [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Oct. 29, 2020 |
| Entity File Number | 001-34877 |
| Entity Registrant Name | CoreSite Realty Corp |
| Entity Incorporation, State or Country Code | MD |
| Entity Tax Identification Number | 27-1925611 |
| Entity Address, Address Line One | 1001 17th Street, Suite 500 |
| Entity Address, State or Province | CO |
| Entity Address, City or Town | Denver |
| Entity Address, Postal Zip Code | 80202 |
| City Area Code | 866 |
| Local Phone Number | 777-2673 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.01 par value per share |
| Trading Symbol | COR |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001490892 |
| Amendment Flag | false |
